A very hard and transparent synthetic form of sapphire used as a watch glass or Crystal. Very scratch-resistant, it has a value of 9 on the Mohs scale of mineral hardness. To give you an idea of its strength, it is used in the shatter proof windows of armoured vehicles.

A commonly used material for watch crystals (which cover and protect the watch face), sapphire crystals are made from synthetic sapphire, which is formed by crystallizing corundum (aluminum oxide) at [..]

Synthetic corundum crystal with a hardness second only to diamond. Transparent sapphire is used for scratch-resistant watch crystals.

The transparent, shatter- and scratch-resistant cover of the watch dial. Made of synthetic sapphire, the hard crystal protects the watch.

A synthetic material used to make watch crystals. Because of its very high hardness (9 on the Mohs scale), sapphire crystal is more scratch-resistant and abrasion-resistant than mineral glass. However, sapphire crystal is also more brittle than mineral glass, and therefore is slightly less resistant to heavy impacts.

Synthetically formed, the sapphire crystal of a watch is extremely scratch resistant (nine on the Moh scale) and is the material of choice for many watch collectors. The downsides are that the sapphir [..]